1. Field of the Invention
The present invention relates to an apparatus for vapour phase epitaxy. For example, such is applicable to the formation of heterostructures intended for the production of electronic components, such as field effect transistors, or optoelectronic components, such as semiconductor lasers.
2. Discussion of the Background
Two groups of vapour phase epitaxy methods are known. According to these, epitaxy is performed on one face of a substrate, which is heated and placed in an epitaxy gas stream flowing in a given direction. More specifically, according to the methods of the first group, the substrate is placed on a fixed support, which is arranged in a reaction chamber parallel to the walls thereof, whilst according to the second group, the substrate is positioned perpendicularly to the direction of the epitaxy gas stream and optionally rotates about an axis parallel to said direction.
The methods of the first group favour a laminar flow of the epitaxy gases, which minimizes the residence time of a given gas molecule in the reaction chamber. The epitaxial layers formed thus have very abrupt composition transitions, which is very favourable to the performances of the electronic components produced from said epitaxial layers. Nevertheless, the methods of the first group suffer from the disadvantage of leading to epitaxial layers, whose thickness and composition are not very uniform. Thus, with these methods, there is a depletion of active substances present in the epitaxy gases in the flow direction thereof. This can be compensated by slightly inclining the substrate support relative to the epitaxy gas flow direction, but this compensation cannot be obtained in a uniform manner over a considerable distance and no matter what the composition of the layers to be deposited.
The methods of the second group make it possible to improve the composition uniformity of the epitaxial layers as a result of a more uniform distribution of the constituents of the gaseous phase on the substrate surface and also due to the fact that it is possible to turn said substrate. Nevertheless, the methods of the second group suffer from the disadvantages of not being able to obtain a radial uniformity of the composition of the layers. In addition, the flow of gases is not laminar, because the substrate and its support constitute an obstacle for the flow of gases. Thus, the residence time of the gases in the reaction chamber is longer, which leads to less abrupt composition transitions in the epitaxial layers than in the case of the methods of the first group.